Dyeing processes for textile webs utilizing reactive dyestuffs are generally known. One process is the so-called extraction process. This is carried out with full-width machines (jiggers) or hank-dyeing machines (reel dyers, jet dyeing machines and the like) with the stepwise addition of dyestuff and alkali to the dye bath, in conjunction with adjustment of the temperature. The disadvantage of this process is that it is discontinuous and can only accommodate limited batch sizes. There is a danger with these earlier systems, moreover, that the ends and edges of the web will be nonuniformly dyed. In addition, these processes are very time-consuming.
A further known process is the so-called two-phase process. In this process the dyestuff is applied by padding with a padding machine or foulard, the padded web is subjected to intervening drying, the alkali is then applied and the dye is fixed by thermal treatment, steam treatment or the lapse of an appropriate holding time. This process has been found to be interesting only for large dye batches since it involves handling between the two application steps.
Another known process is the so-called padding-cold-storage process. This process has, because of its relative simplicity, received great attention in recent years. The dyestuff and alkali are applied in a common dye liquor and the dyed goods are stored for a considerable length of time in a rolled-up state before washing out the excess of the dye so that the dye reaction is complete during the cold-storage state. Because of the instability of alkali dye liquors containing reactive dyestuffs, the dyestuff solution and alkali must be proportionally mixed only shortly before application of the composition by the padding machine or foulard.
Residual dye liquor and the contents of the padding machine are not reusable and create problems when discharged into waste water or with respect to sewage treatment. As a consequence, the use of this process for small or average-sized batches is not rational and, because the process cannot be carried out in a continuous manner, the suitability for large batch dyeing is limited. Nevertheless, the padding-cold-storage process has represented a major advance in reactive piece dyeing to the point that today approximately 70 to 80% of all fabrics dyed with reactive dyes are dyed utilizing this process.
The process has found wide utility because of its great simplicity and in spite of the greater economic and ecological challenge provided by the process.
The padding liquor contains, in addition to the dissolved reactive dyestuff and alkali, high proportions of water glass (Na.sub.2 SiO.sub.3) which is required for stabilizing the reactive composition. The water glass not only provides a substantial load for the waste water but tends to deposit in ducts, pipes and conduits through which the composition may be passed. The residual mixed liquor from the padding machine at the conclusion of the dyeing operation is discharged into waste water and is no longer usable. The water glass tends to deposit upon the padding machine and deflecting rolls to create encrustations and problems
A major disadvantage of the presence of water glass, moreover, is the difficulty which arises in trying to wash out water glass from the fabric after the storage time which can require considerable wash water and energy for the washing process.
Numerous attempts have been made in the past to replace the water glass without success and considerable research is yet under way to attempt to find dyeing processes which do not require the presence of the water glass.